1. Field of the Invention
The present invention relates to a separator for fuel cell which is superior in moldability, electrical conductivity and mechanical strength and which causes no cracking during molding even when made in a small thickness.
2. Description of the Prior Art
As separators for fuel cell, there have been known, for example, (1) a fuel cell separator obtained by subjecting a thermosetting resin to molding, firing and machining; (2) a fuel cell separator obtained by subjecting a dense carbon impregnated with a thermosetting resin, to machining; (3) a fuel cell separator obtained by subjecting a carbon fiber nonwoven impregnated with a conductive coating, to press lamination; (4) a fuel cell separator obtained by kneading a carbon powder and a phenolic resin and molding the kneaded product by hot pressing; and (5) a fuel cell separator obtained by compounding a carbon powder, a phenolic resin and a carbon fiber and subjecting the resulting compound to compression molding.
However, in the fuel cell separator (1) obtained by subjecting a thermosetting resin to molding, firing and machining and the fuel cell separator (2) obtained by subjecting a dense carbon impregnated with a thermosetting resin, to machining, there has been a problem of higher cost incurred by machining and, when the separator is made in a small thickness so as to meet a recent requirement, there has also been a problem of cracking tendency during machining or cell assembling.
In the fuel cell separator (3) obtained by subjecting a carbon fiber nonwoven impregnated with a conductive coating, to press lamination, there has been a problem that the nonwoven hinders formation of surface grooves which are indispensable for fuel cell separators. In the fuel cell separator (4) obtained by kneading a carbon powder and a phenolic resin and molding the kneaded product by hot pressing, there have been problems that moldability and mechanical strength decrease when the ratio of conductive filler is increased in order to increase electrical conductivity and, when the ratio of binder resin is increased in order to increase moldability and mechanical strength, electrical conductivity decreases.
In the fuel cell separator (5) obtained by compounding a carbon powder, a phenolic resin and a carbon fiber and subjecting the resulting compound to compression molding, there is an advantage that a very high strength and a very high elastic modulus can be obtained, but there has been a problem that this high elastic modulus invites somewhat easy cracking when the fuel cell separator is made in a small thickness.